Cathode sputtering apparatus for coating oscillator plates



DeC- 21, 1948. w. H. E. sAMUELsoN CATHODE SPUTTERING APPARATUS FOR COATING OSCILLATOR PLATES Filed 00t- 6', 1945 I INVENTOR /llff ME JNL I BY MM" Patented Dec. 21, 1948 CATHODE SPUTTERING APPARATUS FOR COATING OSCILLATOR PLATES Wallace H. E. Samuelson. Weehawken, N. J.. assignor, by mesne assignments, to Reeves Hoffman Corporation, Carlisle, Pa., a corporation of Pennsylvania.

Application October 6, 1945, Serial No. 620,721

Claims.

This invention relates to the manufacture of quartz oscillator plates and the like and has for its object certain improvements in the apparatus for depositing films of metal on quartz oscillator plates and the like. The invention also has for its object improved quartz oscillator plates as an article of manufacture.

Quartz oscillator plates tend to lose activity on ageing, for example, by being stored. Various treatments of the plates have been proposed to restore the activity of the plates, at least in large part. Among such treatments is that of sputtering the plates with a suitable metal, such as gold. The most common method is to cover the plates completely with a thin layer or coating of gold, not only the surfaces of the two major sides or faces but also the surfaces of the edge portions of the plates. For oscillating purposes, the plates must have high electrical resistance between the surfaces of the two major faces and it is, therefore, necessary to remove the gold from the edges of the plates. This is usually done by abrading the gold from the edge portions of the plates. As a result of the abrading operation, the oscillator plates are frequently scratched, and this in turn impairs their oscillating ch-aracteristics.

The all-gold coated oscillator plates tend to have further undesired characteristics. For eX- ample, they tend to have a lower activity than that of the uncoated, but unaged, plates. Some of the coated oscillator plates also tend to oscillate with a spurious frequency. This latter trait is especially detrimental because its occurrence is erratic, unpredictable and not necessarily reproducible even in the same oscillator plate.

An uncoated quartz oscillator plate which eX- hibits no spurious frequency may show one or more after being covered with gold.

As a result of my investigations, I have discovered that if the quartz oscillator plates are coated with metal in a certain manner, disadvantages of the kind enumerated may be largely overcome. The thin film, coating or layer of metal may be deposited on the oscillator plates in such a manner as to make unnecessary the customary abrading operation on the edge portions and thus minimize greatly the chances of scratching or otherwise imparing the two main surfaces of the oscillator plates.

In accordance with the apparatus of the present invention, a support for the oscillator plates is positioned within a chamber, the support'being provided with a hole of predetermined size across which a plate may be rplaced in contact 2 with the support so that the part of the plate exposed. through the hole will be covered with a film of the metal to be deposited while the unexposed surface of the plate in contact with the support will not be covered with a lm of metal.

The two main sides or surfaces of the oscillator plates are advantageously covered simultaneously with metal in the manner indicated. This can be done in such a way that the side of the plate containing the spot will contain no metallic deposit other than the spot. This spot is advantageously located centrally of the, oscillator plate and is preferably of predetermined size, depending upon the size and intended use of the oscillator plate.

In a presently preferred practice of the invention, the metallic films are deposited on the osclllator plates by means of a high voltage across a metal anode and one or more metal cathodes operating in an evacuated chamber having the necessary electrical connections. The cathode disintegrates and the metal of which it is made is deposited or tends to deposit upon the anode as an extremely thin and homogeneous film. A flat sheet or plate of aluminum is advantageously employed as the anode, the anode being punched with a plurality of spaced holes of a size corresponding to the metallic spots to be placed on the oscillator plates. are advantageously made of gold. The anode plate is horizontally disposed and equidistantly spaced between a pair of the' cathodes in a present practice of the invention.

The oscillator plates are placed on the aluminum anode, each plate being centered over one of the holes in the anode. The upper surface of each oscillator plate is completely exposed, as is so much of the lower surface of each oscillator plate over the holes. The remainder `of the lower surface of the oscillator plates is in contact with the aluminum anode and is, therefore, masked olf. v

The chamber is evacuated in the usual manner and high voltage current is passed across the anode and cathodes. This causes the gold in the fore, deposits a film on the exposed upper'surface of the oscillator plates and so much of the under surface of the oscillator plates as is ex` posed by the holes in the aluminum anode.

The invention will be better understood by referring to the accompanying drawing, taken The cathodes` ductor.

in conjunction with the following description, in which- Fig. 1 is a side elevation in section on the line I--I of Fig. 2 of an apparatus illustrative of a practice of the invention;

Fig. 2. is, aV plan. View partly in section. and partly in fragmentary' sections of theY same apparatus;

Fig. 3 is a diagrammatic representation of the internal arrangement of the apparatus;

Fig. 4 is a plan view with aout-away portion; of a quartz oscillator plate treated. in. the apparatus;

Fig. 5 is an enlarged end, View, off. the quartz oscillator plate of Fig. 4;

Fig. 6 is a sectional elevation in part of an anode and a mask for a modied` practice; and

Fig. '7 is an enlarged end view'off the quartz oscillator plate of Fig. 6.

Referring first to Fig. v1, the apparatus shown comprises a glass bell-jar or cover I0, defining. a chamber I I. The lower circumferential edge portion I2 of the bell-jar lits snuglywithin an annularl groove I3 of a rubber gasket I4 resting on a metal base I5. The bell-jar and: rubber gasket are readily removable as a unitl from the. steel base. One end of. a conduit I6 is non-leakably screwed' into an opening IT in base I5, thus communicating with chamber II, andthe other end of the conduit connects with a source, of. vacuum, not shown.

The parts located within chamber I'I. comprise a pair of spaced metallic c athodes` 2D. and. 2.I and a metallic. anode 22 midway betweenthe two, alli horizontally, disposed. to, base I5'. Ina presently preferred' practice, thel cathodes are formed of gold. and the anode. of aluminum. Thus, upper cathode 20,is formedof. a. thinsheet of gold or gold foil 23 underlying an appropriately. supported upper aluminum plate 24,4 the overlying edge portion. 25; of. the gold sheetl being. bent upwardly and over the top of the edgeportionsof a glass plate 26-resting onthe topof the upper. aluminum plate.v Inv similar fashion, lower cathode 2l isv also. formed ora. thin sheet of goldlor gold foil 21 overlying an, appropriately. supported lower aluminum. plate. 28, the. overlying edgeportion 29 ofthe gold sheet being bentdowny Wardly andover the topof the edge portion of an. appropriately supported` glass plate 39 located immediately below the lower aluminum plate.

As shown, upper aluminumV plate 2,4. andlower aluminum plate 28Y are held in position. by two oppositely located Vertical. supports 35l and 3B, the former being provided with an electrical con- Thus, support 35'consists of. a vertically disposed conductor rodS'I. threadedat` both ends.

thelower end ofwhichA extends through arropen.

ingl in` base I5.- and thel upper endl of which; extendsthroughl a. slotted openingk 38 in ashoulder portion 39.0f upper aluminumplate24. Theron-- ductor rod'isheld in position by means of a nut 40 secured well above the lower end of,e the rod,. aninsulating Washer 4-I= being disposed between the nuty and they lower side of baseA I5, and a truncated porcelain insulator 42, the lower portion of Whichis reduced in size tot snugly in the same` opening of the base. through which therod extends, thus` forming a shoulder portion 43i resting upon the base. The truncated porcelain insulator fits around an enlarged lower, section of the conductorvrod,` the upper end of the enlarged section being threadedto receive az stop nutA` 44. The conductor rod extends throughv a. slotted, opening vin a shoulderportion.

45 of lower aluminum plate 28 which rests on the nut. A cylindrical porcelain insulator 46 fits around the upper and reduced section 4l of the conductor rod, the lower end of the insulator resting on the top of shoulder portion d5 of lower aluminum. plate 28. Theupper end oi the insulator terminates at the upper threaded end of the conductor rod. Shoulder portion 39 of upper aluminum plate 24 is located on the upper end of the insulator and is secured thereto by means offa nut48 turnedtightly on the upper threaded portion of thev conductor rod.

Vertical supportr 3.6 is advantageously constructed in the same manner as vertical support It is` therefore unnecessary to describe its construction in detail. It consists of a rod 55 threaded at. both ends to receive nuts 55 and 51, and thereby hold in place truncated insulator 58, nut;59', slotted shoulder 60 of lower aluminum plate 28, cylindrical insulator 6l and slotted shoulder. 62.01. upper aluminum plate 24. 1n the ccnstruction shown, however.. vertical support. 35 is not. designed toformpart of an electrical circuit.

Returning. tov verticalsupport 35, its electrical connection isprovided by means ofA a` highvoltage line 65, connectiblewithv a source of current, not shown, and a terminal `66 secured. to conductor rod 3l. The terminal is disposed between nut Mland a securing nutl El. on* the lower endl of the conductor rod.

Turning neXtv to anode 22, itl will. be notedthat itis held in position by three. spaced vertical` supports l0, 'll and 12. They are.Y similar in construction, except that. the, latter isconnectible electricallywith thesourcefoi high voltage current to be employed. Thus; verticalsupport 'l2- con.- sists of aY vertically disposed conductor rod- 13 threaded at both4 ends, theA lower end ofwhich extendsy through an opening in base I5 andthe upper end` ot which extends through a slotted opening. 'Id in'v a shoulder portion i/offaluminum4 plate 22. IIvhe conductor rod is heldiinV position by means. of anut 'I6 secured to thev lower. end of the rod,v anV insulating, bushing 11, whichaits snugly in. the. hole in thebase, a cylindrical-poncelain insulator 'I8 and a nut. 19: secured to the;

upper end of the conductor rod. The, electrical connectionV is. providedby means of 1 a: high voltage line 80, connectible.with the source-of highvoltage current, anda terminalk 8l.; The terminal is disposedbetween nut. 'I5 and'insulating bushing/ll?.

Still referring tol anode: 225, which-,1 as, stated.. is an. aluminum plate', in` apresently preferred practice of the invention, it will' be noted. that its` top portion is` subdividedv into a plurality 0f rectangular recessesspaced from one another by' relatively narrowY crissecross; top.y portions 86 ofA the aluminumplate.. The: rectangular. recesses are preferably of?. a size easily to accommodate rectangular` quartz oscillator plates. Si. While rectangular-recesses arezshown', it willibe obvious` that theyv may: be circular or in other desired: conguration'. In' the constructionshown, eachV recess isy providedv withA ay centrally located hole 88', preferably o f; predeterminedy size so. as` to.A

showninpart; It may be desirable to sputter. a`v

spot.V onibothy. major faces; of the oscillator plates..

This may be accomplished, for example, by placing. a mask 89 on the top of anode 22, the mask being provided with a plurality of suitably spaced holes 90, preferably juxtaposed to holes 88 in the anode proper.

Glass plate 30, which is located immediately below and preferably in contact withl lower aluminum plate.28 forming a part of the lower cathode construction, is freely supported on three vertically disposed and spaced supports 9|, 92 and 93, resting on base |5. The supports may, for example, be formed of cylindrical porcelain, such as used in the other vertical supports. The supports for the glass plate may merely rest on the base, although they may be secured thereto, if desired,

The apparatus described may be operated as follows in the practice of the invention:

With bell-jar I0 removed, a quartz oscillator plate 81 is placed in each recess 85 of anode 22. The bell-jar is then returned to cover the anode-cathodes-assembly and chamber is evacuated through conduit |6 to a suitable subatmospheric pressure. High voltage current is next applied across terminals 66 and 8| and thus across cathode 20 and anode 22 and across anode 22 and cathode 2|. This causes gold foil 23 of cathode 20 and gold foil 21 of cathode 2| gradually to disintegrate, filling chamber with sputtered gold vapor. deposited on exposed surfaces of the quartz oscillator plates to form a thin and homogeneous film. The top and edge and the bottom circular spot surfaces, being the only portions of the oscillator plates thus exposed, are therefore covered with gold in this manner. After a suitable interval of time, enough to deposit the desired amount of gold, the application of current is discontinued and the vacuum broken; after which the bell-jar is removed and the treated oscillator plates are removed. In Figs. 4 and 5, the deposit is shown as a top and edge lm 95 and a bottom spot 96.

If, on the other hand, it is desired to sputter a spot on each major face of oscillator plates 81, mask 89 is placed on the top of anode 22, As sputtering of gold from cathodes 20 and 2| takes place, spots 89' are also placed on the oscillator plates. Portions of the oscillator plates covered by the mask will then obviously not be sputtered with the gold. When the spots are centered in the manner indicated, they provide electrode contacts, which brings the electric field to the center of the oscillator plates where it does the most good.

While in the practice described above high voltage cathode sputtering is employed, it will be clear to those skilled in this art that other means may be employed to deposit the film of metal in the manner desired. Arc sputtering may also be used.. Pencils of the metal to be deposited may be brought together with a suitable electromotiveforce applied between them. A voltage may be applied between the cathode of the arc and the oscillator plate to cause the metal ions to pass over the exposed surface of the plate to be coated. Various evaporation methods may be employed, such as distillation of the metal to be deposited from a heated container in the chamber, or thermal evaporation of the metal, for example, as a coating from heated tungsten filament. It will thus be clear to those skilled in this art that the practice of the invention lends itself readily to a number of highly useful modifications.

I claim:

1. In apparatus for d-epositing films of metal -on Some of the gold vapor is Y 6 quartz oscillator plates and the like, means de;- fining a chamber, a pair of vertically spaced cathodes in said chamber and ofthe metal to be deposited, anv anodic support in said chamber for 'the plates having an upper plate supporting surface, said support horizontally disposed and located substantially midway between said cathodes, said support provided with a vertically ex-A` tending hole of a size across which a plate may be disposed with the plate in con-tact with said upper surface of the support about said h-ole whereby that portion of the lower. face ofthe plate -exposed through the hole vand the entire upper face of the plate will be cov-ered with lms of metal from said cathodes.

2. In apparatus for depositing films of metal on quartz oscillator plates and the like, means defining a chamber, a pair of vertically spaced horizontal flat sheet cathodes in said chamber and of the metal to be deposited, a flat sheet anodic support in said chamber for the plates having an upper plate supporting surface, said support horizontally disposed and located substantially midway between said cathodes, said support being provided with a plurality of vertically extending holes each of a size across which a plate may be disposed with the plate in contact with the portions of .the upper surface of the support about Ithe holes whereby the portions of the lower faces of the plates exposed through the holes and the entire upper faces of the plates will be covered with films of metal from said cathodes.

3. The apparatus as in claim 2 including a mask i provided with a plurality of holes, said mask disposed on the upper side of said anodic support and having its respective holes in alignment with the upper faces of the respective plates whereby such upper faces will be covered with lms only on their portions expo-sed through the holes in the mask.

4. In apparatus for depositing films of metal on quartz oscillator plates and the like, means delining a chamber, a pair of vertically spaced cathodes in said chamber and of the metal to be deposited, a horizontally dispos-ed anodic support within said chamber for Ithe plates having an upper plate supporting surface, said support located between said cathodes, and said support being provided with a vertical hole therethrough opening downwardly to the lower cathode and of a size across which a plate may be positioned in contact with said upper surface of the support and with a Portion of the lower face of the plate exposed through said hole whereby of the lower surface Iof the plate only that portion exposed through said hole will be covered with a film of metal from said cathode and whereby the upper side of said supported plate is not obstructed by -said support.

5. In apparatus for depositing films yof metal on quartz oscillator plates and the like, means defining a chamber, a pair of vertically spaced horizontal fiat `sh-eet cathodes in said chamber and of the metal to be deposited, a flat sheet anodic support within the chamber for the plates having an upper plate supporting surface, said support arranged horizontally within the chamber and between and substantially parallel with said cathodes, upstanding partition walls upon the upper surface of said anodic support subdividing it into a plurality of recesses each adapted to receive an oscillator plate, and said support being provided with a vertical holev within each of said recesses inwardly of its partition walls whereby the plates located in said recesses will have the portions of their lower surfaces exposed through said 

